The present invention is generally directed to ink jet printers. More particularly, the invention is directed to a system for improving print quality by compensating for misalignment or skew between various components in an ink jet printer.
Many ink jet printers form printed images on a print medium by ejecting droplets of ink from ink nozzles on a print head as the print head is scanned across the print medium. Ink droplets are formed and ejected from the nozzles when the ink is super-heated by resistive heating elements disposed on a heater chip in the print head. Typically, the print head rides on a carriage that scans the print head horizontally across the print medium to print a swath of the image. At the end of a swath, the print medium is advanced by the width of the swath, and the print head is again scanned across the print medium to print the next swath of the image.
Typically the nozzles on the print head form an array that is aligned perpendicular to the scan direction. The length of the array generally defines the width of the swath. If the nozzle array is not perfectly perpendicular to the scan direction, visible print defects may occur at each swath-to-swath boundary in the printed image. This problem is more pronounced as nozzle counts and swath widths increase.
Several factors contribute to misalignment between the nozzle array and the scan direction. These include misalignments between the heater chip and the body of the print head cartridge, and between the print head cartridge and the carriage rail.
This problem has been addressed mechanically by attempting to maintain manufacturing tolerances to keep misalignments within an acceptable range. However, this approach requires expensive precision components and equipment to manufacture both the print head and the carriage. Prior attempts at electronic timing adjustments to compensate for the misalignment have proven to be cost prohibitive and size prohibitive due to large amounts of logic required per nozzle.
Therefore, a system is needed for adjusting the timing of ink ejection from nozzles or groups of nozzles in a manner that reduces swath-to-swath skew to an imperceptible level, while taking into account mechanical, electrical, fluid flow, and cost restraints.
The foregoing and other needs are met by a method for compensating for misalignments in an ink jet printer having an ink jet print head cartridge that includes a heater chip. The method includes determining alignment adjustment information related to the misalignments in the ink jet printer, loading the alignment adjustment information into a volatile memory device on the heater chip, and accessing the alignment adjustment information from the volatile memory device. The method also includes generating nozzle control signals based at least in part on the alignment adjustment information. The nozzle control signals are selectively provided to resistive heating elements in the heater chip, thereby heating ink in ink chambers adjacent the heating elements and ejecting ink droplets toward a print medium.
The timing of the nozzle control signals is adjusted based upon the amount of misalignment in the various components of the printer and print head. Preferably, the timing adjustments are applied to groups of nozzles so that dots printed by one group are substantially vertically aligned with dots printed by another group, thereby reducing the amount of perceptible skew in the printed output.
Preferred embodiments of the method include the steps of storing heater chip alignment information in a print head memory device on the ink jet print head cartridge, and storing print head alignment information in a printer memory device in the ink jet printer. In these embodiments, the alignment adjustment information is determined based at least in part on the heater chip alignment information stored in the print head memory device and the print head alignment information stored in the printer memory device.
In another aspect, the invention provides an ink jet printer for forming printed images on a print medium based on print data. The printer includes a carriage that is movable in a first direction relative to the print medium, and an ink jet print head cartridge mounted on the carriage. The print head cartridge includes a cartridge housing that is mechanically coupled to the carriage, where the cartridge housing is oriented with respect to the carriage according to a print head alignment angle. The cartridge also includes an ink jet heater chip oriented with respect to the cartridge housing according to a heater chip alignment angle. The ink jet heater chip has an array of resistive ink-heating elements, and a heater chip memory device for receiving alignment adjustment information. The print head cartridge further includes a print head memory device for storing heater chip alignment information related to the heater chip alignment angle. An array of ink-ejection nozzles is provided on the print head cartridge corresponding to the array of ink-heating elements.
The printer includes a printer controller having a printer memory device for storing print head alignment information related to the print head alignment angle. The printer controller incorporates control electronics that are electrically coupled to the heater chip memory device, the print head memory device, and the printer memory device. The control electronics access the print head memory device to retrieve the heater chip alignment information, access the printer memory device to retrieve the print head alignment information, determine the alignment adjustment information based at least in part on the heater chip alignment information and the print head alignment information, and provide the alignment adjustment information to the heater chip memory device.